In the past, sensing of vibration in aircraft engines was more of an art than science. For example, a pilot felt for vibration in the throttle handles, through the pilot's seat, or even noticing that ripples in the pilot's coffee were agitated more than normal. Often, aircraft vibrations were extremely difficult to duplicate for ground mechanics. As a result, flying mechanics on aircraft was a common practice to illustrate that there was a vibration problem on the aircraft and to prove to ground crews that the aircraft truly had a problem.
Increasing complexity of aviation systems over the years has caused greater confusion among flight crews as to what actually was the source of the vibration. More often than not the flight crew would blame the engine as the cause of the vibration. Due to escalating costs of engine removal and repair of the engine off the aircraft, there is a great reluctance to remove an engine from an aircraft and a greater need for monitoring general engine health.
The Federal Aviation Administration has required operators flying within United States airspace to have engine vibration monitoring equipment installed and operable on all commercial aircraft. The currently known method of measuring engine vibration is to utilize two transducers. One transducer monitors the fan section of the engine and is mounted directly onto the fan. A second transducer monitors the high-pressure section, or core, of the engine and is mounted aft over the core. The transducer output is a spurious direct current output that is input into a charge amplifier. The charge amplifier amplifies the input and multiplies the input by a sine wave that is set at a known frequency. Generally, the charge amplifier is mounted in the engine pylon.
The output of the charge amplifier is run through twisted wire, shielded pair that terminates in a control box in the avionics bay. The signal processing for the engine vibration system is computed within the control box, where a Fourier Transform of the vibration is taken. The Fourier Transform of the engine vibration for the fan is the amount of vibration of the fan divided by the fan speed. The Fourier Transform of the engine vibration for the high-pressure turbine is the turbine vibration divided by the turbine speed. Recent advancements in monitoring engine vibrations include use of a fan-tracking filter that samples the speed of the turbo-fan and an engine core speed-tracking filter that samples the speed of the engine core. The introduction of these filters has increased the reliability of the engine vibration monitoring system.
The output of the control box is a numeric display viewable by the pilot. This numeric display is represented in mils ( 1/1000 inch) of engine displacement. Accordingly, present indications of engine vibration monitoring systems are limited to providing flight crew information in numbers or bar indicators that offer a limited amount of information to the flight crew.
As such, current aircraft engine vibration monitoring systems do not provide flight crews and ground maintenance crews with information about engine health. This can lead to guessing by the flight crews and ground maintenance crews as to whether the engine vibration monitoring system is providing proper vibration alerting. Further, ice build-up on fan sections of aircraft can cause damage to engine acoustical panels or, in extreme cases, severe damage to compressor sections of the engine and or engines.
Because aircraft engines are high dollar assets, repairs are costly and operators are reluctant to take engines off-wing in response to false alerts from the vibration monitoring system. In an extreme case, this may lead to catastrophic failure.
As a result, ground crews may be reluctant to trust vibration-monitoring equipment that gives them inadequate information about engine health. Further, it is impractical to present the flight crew with a frequency spectrum and ask the flight crew to make decisions based on their inference of the spectrum. Thus, there is an unmet need in the art for an aircraft engine vibration system that provides information about engine health.